Displaying Nested Relational Data
Displaying Nested Relational Data:
example:
结果：
Professional ATL Com
ISBN: 1861001401 Release Date: 1998-8-20 0:00:00
Author(s): Richard Grimes,
Price: CAN:83.95 GBP:55.49 USD:59.99
Beginning Visual Basic 5 Objects
ISBN: 1861001452 Release Date: 1998-4-1 0:00:00
Author(s):
Price: CAN:48.95 GBP:32.49 USD:34.99
Professional MTS & MSMQ Programming With VB And ASP
ISBN: 1861001460 Release Date: 1998-5-1 0:00:00
Author(s): Alex Homer, David Sussman,
Price: CAN:69.99 GBP:46.99 USD:49.99
关键代码：
<wrox:connect id="ctlConnectStrings" runat="server"/>
<%-- insert the control that creates the DataSet --%>
<wrox:getdataset id="ctlDataSet" runat="server"/>
<div id="divResults" runat="server"></div>
<script language="C#" runat="server">
void Page_Load(Object sender, EventArgs e)
{
// get connection string from ..\global\connect-strings.ascx user control
string strConnect = ctlConnectStrings.OLEDBConnectionString;
// create a variable to hold an instance of a DataSet object
DataSet objDataSet;
// get dataset from get-dataset-control.ascx user control
objDataSet = ctlDataSet.BooksDataSet(strConnect, "ISBN LIKE '18610014%'");
if (objDataSet == null)
return;
// now we're ready to display the contents of the DataSet object
// create a string to hold the results
string strResult = "";
// create a reference to our main Books table in the DataSet
//创建datatable
DataTable objTable = objDataSet.Tables["Books"];
// create references to each of the relationship objects in the DataSet
//得到datarelation .BookAuthors,BookPrices是关系名
DataRelation objAuthorRelation = objTable.ChildRelations["BookAuthors"];
DataRelation objPriceRelation = objTable.ChildRelations["BookPrices"];
// now we can iterate through the rows in the Books table
//叠代DataRow
foreach (DataRow objRow in objTable.Rows)
{
// get the book details and append them to the "results" string
strResult += "<b>" + objRow["Title"] + "</b><br /> ISBN: " + objRow["ISBN"]
+ " Release Date: " + objRow["PublicationDate"] + "<br />";
// get a collection (array) of all the matching Author table rows for this row
//利用GetChildRows方法取得当前行的所有子表中匹配的行集合（以ISBN为匹配标准）objAuthorRelation是关系。类似的，也可以用GetParentRows方法取得当前行的所有父表中匹配的行集合。当然，这样的话就不是以Book名作为显示次序了。而是以作者名称或者价格作为显示次序了。
DataRow[] colChildRows = objRow.GetChildRows(objAuthorRelation);
strResult += " Author(s): ";
// iterate through all the matching Author records adding to the result string
//遍历所有子表中匹配的行集
foreach (DataRow objChildRow in colChildRows)
strResult += objChildRow["FirstName"] + " " + objChildRow["LastName"] + ", ";
strResult += "<br />";
// repeat using the Price table relationship to display data from matching Price records
//类似的处理价格子表中匹配的行集
colChildRows = objRow.GetChildRows(objPriceRelation);
strResult += " Price: ";
foreach (DataRow objChildRow in colChildRows)
strResult += objChildRow["Currency"] + ":" + objChildRow["Price"] + " ";
strResult += "<p />";
}// and repeat for next row in Books table
divResults.InnerHtml = strResult; // display the results
}
</script>
DataSet BooksDataSet(string strConnect, string strWhere)的定义：
public DataSet BooksDataSet(string strConnect, string strWhere)
{
outConnect.InnerText = strConnect; //display connection string
// specify the SELECT statement to extract the BookList data
string strSelectBooks = "SELECT * FROM BookList WHERE " + strWhere;
outSelectBooks.InnerText = strSelectBooks; // and display it
// specify the SELECT statement to extract the BookAuthor data
string strSelectAuthors = "SELECT * FROM BookAuthors WHERE " + strWhere;
outSelectAuthors.InnerText = strSelectAuthors; // and display it
// specify the SELECT statement to extract the BookPrices data
string strSelectPrices = "SELECT * FROM BookPrices WHERE " + strWhere;
outSelectPrices.InnerText = strSelectAuthors; // and display it
// declare a variable to hold a DataSet object
// note that we have to create it outside the Try..Catch block
// as this is a separate block and so is a different scope
DataSet objDataSet = new DataSet();
try
{
// create a new Connection object using the connection string
OleDbConnection objConnect = new OleDbConnection(strConnect);
// create a new Command object
OleDbCommand objCommand = new OleDbCommand();
// set the properties
objCommand.Connection = objConnect;
objCommand.CommandType = CommandType.Text;
objCommand.CommandText = strSelectBooks;
// create a new DataAdapter object
OleDbDataAdapter objDataAdapter = new OleDbDataAdapter();
// and assign the Command object to it
objDataAdapter.SelectCommand = objCommand;
// get the data from the "BookList" table in the database and
// put it into a table named "Books" in the DataSet object
objDataAdapter.Fill(objDataSet, "Books");
// change the SELECT statement in the ADOCommand object
objCommand.CommandText = strSelectAuthors;
// then get data from "BookAuthors" table into the DataSet
objDataAdapter.Fill(objDataSet, "Authors");
// and do the same again to get the "BookPrices" data
objCommand.CommandText = strSelectPrices;
objDataAdapter.Fill(objDataSet, "Prices");
//以上为Dataset创建了三个表
// declare a variable to hold a DataRelation object
DataRelation objRelation;
// create a Relation object to link Books and Authors
//定义名为BookAuthors的关系：Books表为父表，Authors为子表，ISBN是连接标准
objRelation = new DataRelation("BookAuthors",
objDataSet.Tables["Books"].Columns["ISBN"],
objDataSet.Tables["Authors"].Columns["ISBN"]);
// and add it to the DataSet object's Relations collection
//添加关系
objDataSet.Relations.Add(objRelation);
// now do the same to link Books and Prices
//类似处理另一个关系
objRelation = new DataRelation("BookPrices",
objDataSet.Tables["Books"].Columns["ISBN"],
objDataSet.Tables["Prices"].Columns["ISBN"]);
objDataSet.Relations.Add(objRelation);
}
catch (Exception objError)
{
// display error details
outError.InnerHtml = "<b>* Error while accesing data</b>.<br />"
+ objError.Message + "<br />" + objError.Source;
// return Nothing on error
return null;
}
// display a success message
outError.InnerHtml = "DataSet created and loaded.";
// return our new disconnected DataSet object
return objDataSet;
}